High pressure turbine blades have increasingly complex geometries particularly with internal channels for cooling them by air circulation, internal partitions and a curvature called variable. After manufacture, the thickness of the outer walls in line with the channels must be evaluated by a nondestructive method in order to ensure their mechanical strength. The uncertainty of the measurement must be low. For example, for wall thicknesses ranging from 0.3 to 1.2 mm an uncertainty of less than 25 micrometers is set.